Chiral effective field theory (\(\chi \) EFT) is the leading effective theory describing the first level of complexity emerging
from the Standard Model, viz how the fundamental quarks and gluons produce hadronic and nuclear phenomena.
As such, \(\chi \) EFT is a crucial component of our global understanding of Nature. It has been very successful in
explaining hadronic and nuclear physics [1]}. Yet, its description of
nucleon spin structure remains imperfect. Table REF  (adapted from [2]}) lists nucleon spin observables measured in the late 1990s and early 2000s at Jefferson Lab (JLab)
and shows how well the \(\chi \) EFT predictions available at the time described them.
(What the observables mean is unimportant here. Their definitions will be given in latter sections.)
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